Actually it is 25 fps scrolling... if you want to see how actual 50fps scroll looks like maybe check this out:

[ Show youtube player ]

It is not. The game is running at 50 fps. It's not a 25 fps scrolling.

check here :

"You get detailed mode-0 16 color graphics, ultra-smooth and fast scrolling which runs constantly at 50 frames per second, fast-moving and well animated sprites and nice in-game music which changes dynamically with the action!
Although the game is very short it still can make every CPC fan proud as it shows what our beloved machine can deliver if it is programmed by the right people."